Another possibility - if there is a cooperative person on the other end, see if you can install the free version of LogMeIn on their computer and yours. This gives you local access to the remote modem from its LAN side. Remote WAN login may be disabled. This worked well for me when I was dealing with a non-technical (but friendly) user in a foreign country. If the modem still has the original factory login settings, they may be on a sticker on the bottom.
Hope this helps...